In the construction and engineering fields it is common practice to dig trenches to lay water and sewer pipes, foundations, cables or the like. Typically, these trenches can be rather deep and require the physical entry of personnel who are installing the sewer pipe, foundation, cable or the like. To prevent cave-in or collapse of a freshly dug trench, the side walls of the trench are lined with shoring boards such as plywood or a similar material and then supported using what is commonly known in the industry as a trench brace or shoring jack. The shoring jack must be capable of extending to hold the shoring boards securely against the walls of the trench, and then locking in the extended position in order to prevent the shoring walls from collapsing.
Conventional shoring devices of this type include a cylinder and piston which form a hydraulically extendable actuator. The piston is connected to a elongated spherical piston rod which is reciprocal within the cylinder. The cylinder in turn is fitted with a hose for introducing hydraulic fluid into the cylinder thereby forcing the piston to extend relative to the cylinder.
In the past, shoring devices have been equipped with external mechanical locking means which consisted of a round threaded piston rod and a nut. The nut was threadedly connected to the piston rod and engaged the cylinder thus preventing contraction of the piston rod with respect to the cylinder. Such devices are shown in U.S. Pat. Nos. 891,897, 2,408,181, 3,905,279, and 4,787,781.
Another such shoring device utilized an internal mechanical locking means which consisted of a round threaded piston rod coaxially surrounded by a tubular sleeve. The tubular sleeve included an annular member provided with a male thread on the outer surface and a female thread on the inner surface. A nut cooperated with the outer surface of the annular member and acted to secure the threaded piston rod. Examples of this type of shoring device are found in U.S. Pat. Nos. 4,247,082 and 4,449,734.
However, in shoring devices of the type mentioned above, the threaded portion of the extendable piston rod collects dirt and other foreign particles which, upon reciprocating back into the cylinder, jeopardizes the integrity of the hydraulic seals. It is particularly this problem, among other things, that the present invention addresses.